The Federal Drug Administration requires that the peak rarefractional pressure of an ultrasonic beam entering a patient be below a specified level. To ensure this requirement is met, medical diagnostic ultrasound imaging systems often display the mechanical index, which is related to the peak acoustic pressure in the imaging field. The displayed mechanical index can also be used to set-up and conduct a contrast imaging examination. The non-linear response (harmonics or destruction) of contrast agents is dependent, in part, on the acoustic pressure of an ultrasonic wave. If a non-linear response is not desired, a user of the ultrasound system can reduce the transmit power, for example, to reduce the displayed mechanical index to a level that will minimize undesired responses in the contrast agent. However, the displayed mechanical index may not be related to the location in the imaging field where the contrast agent is present. Accordingly, the use of the displayed mechanical index is often only a crude measure of the relevant pressure and can result in sub-optimal imaging conditions. For example, a user may reduce the transmit power to a level lower than needed to avoid a non-linear response from the contrast agent, thereby making an unnecessary sacrifice in image quality. Also, with the current approach, multiple injections of contrast agent into a patient may be needed to optimize the imaging procedure. Additionally, the spatial ambiguity associated with the displayed mechanical index can result in error when comparing the response of contrast agent from two regions of interest.
There is a need, therefore, for a medical diagnostic ultrasonic imaging system and method that overcomes the disadvantages described above.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims.
By way of introduction, the preferred embodiments described below provide a medical diagnostic ultrasound imaging system and method for determining an acoustic output parameter of a transmitted ultrasonic beam. In one preferred embodiment, the ultrasound system determines an acoustic output parameter of a transmitted ultrasonic beam in a user-selected region. In another preferred embodiment, the ultrasound system achieves a specified acoustic output parameter of a transmitted ultrasonic beam in a selected region by automatically adjusting an operating parameter of the ultrasound imaging system. In yet another preferred embodiment, a region is selected in the ultrasound image that does not contain a peak acoustic output parameter of a transmitted ultrasonic beam. The system then determines an acoustic output parameter of the transmitted ultrasonic beam in that region and provides an indication of the determined acoustic output parameter.
The preferred embodiments will now be described with reference to the attached drawings.